It is desired to make deep pores with high aspect ratio in a silicon substrate on manufacturing fields of a trench capacitor in a semiconductor memory (Patent Reference 1), a penetration electrode in a three-dimensional packaging (Patent Reference 2) a nozzle plate in an inkjet printer (Patent Reference 3) and so on. For methods to make such deep pores with high aspect ratio, the reactive ion etching method (Patent Reference 4) and the electrochemical etching method (Patent Reference 5, Nonpatent Reference 1, 2) are known.
In the reactive ion etching (RIE) method, a patterned hard mask is laid on a monocrystalline substrate to be etched in a plasma reaction chamber. Then, sidewall protection deposit is accumulated during etching to limit the opening width of the hard mask. Therefore, it became difficult for reactive etchant ion to reach the substrate through the size reduced opening, and a process for reducing the thickness of the side wall protection deposit is required.
In the electrochemical etching method, while a substrate is being contacted with electrolyte, positive voltage has to be externally applied to the substrate.
Patent Reference 1: Published Japanese translation of a PCT application No. 2004-514276
Patent Reference 2: Japanese Unexamined Patent Application Publication No. 2004-95849
Patent Reference 3: Japanese Unexamined Patent Application Publication No. H11-268281
Patent Reference 4: Japanese Unexamined Patent Application Publication No. 2002-367960
Patent Reference 5: Japanese Unexamined Patent Application Publication No. H6-326077
Nonpatent Reference 1: Thin Solid Films, 1997, 297, 13-17
Nonpatent Reference 2: J. Electrochem. Soc., 1999, 146, 2968-2975
Nonpatent Reference 3: Nikkan Kogyo Shinbun (issued on Apr. 22, 2005)
Nonpatent Reference 4: Adv. Mater., 2005, 17, 1045-1047
Nonpatent Reference 5: Angew. Chem. Int. Ed. 2005, 44, 2737-2742
Nonpatent Reference 6: Appl. Phys. Lett., 2000, 77, 2572-2574